PROJECT SUMMARY The brain regulates the reproductive axis via gonadotropin-releasing hormone (GnRH) neurons. GnRH neurons are themselves regulated by ?upstream? neural circuits, but the mechanisms underlying this are still not well known, especially before adulthood. In particular, the processes timing the activation and progression of pubertal development in either sex are poorly understood. How is puberty triggered, and why does it occur when it does? Why do girls enter puberty before boys? These fundamental questions remain unanswered. Recently, the neuropeptide kisspeptin was linked to puberty and fertility. Yet, the precise roles and regulation of the various kisspeptin neural populations in puberty are still poorly understood, as is the timing or necessity of kisspeptin signaling at unique pubertal stages. Moreover, potential sex differences in pubertal kisspeptin timing and action, which may relate to known sex differences in normal puberty and pubertal disorders, are completely unexplored. This proposal uses mouse models to study the functional roles and potential interplays of kisspeptin and inhibitory neural signaling factors, dynorphin and GABA, in puberty control in both sexes. Aim I illuminates the precise temporal and neuroanatomical roles of endogenous kisspeptin signaling before and during key stages of puberty in males and females. Aim I determines 1) whether short-term blockade or enhancement of kisspeptin neuronal firing during key developmental times alters puberty onset or completion and if this differs between the sexes, 2) the necessity of discrete neuroanatomical kisspeptin populations for pubertal onset and progression in each sex, and 3) the molecular profile of peripubertal kisspeptin neurons to ascertain how known reproductive genes and novel identified genes specifically in Kiss1 neuronal populations change their expression with puberty, and whether this differs between sexes. Aim II studies the role of the inhibitory neural factors, dynorphin and GABA, in puberty onset and progression in both sexes. These factors have been implicated in suppressing adult GnRH/LH secretion, but it is unknown to what degree dynorphin or GABA are involved in pubertal timing in either sex or whether they interact directly with kisspeptin neurons to coordinate puberty. Aim II tests 1) if blockade of endogenous dynorphin or GABA signaling advances pubertal onset or completion in males or females, 2) whether endogenous dynorphin or GABA signaling occurring directly in kisspeptin neurons is necessary for normal puberty onset and/or progression in either sex, and 3) whether endogenous dynorphin or GABA signaling comprise a key component of the neural suppression of prepubertal kisspeptin neurons in a sex specific manner to help time puberty onset. Overall, this proposal using cutting-edge transgenic, chemogenic, pharmacologic, and molecular profiling techniques in both sexes to provide new insight into the neural mechanisms?including both stimulatory and inhibitory factors?underlying the triggering and timing of normal puberty and pubertal disorders, which are both sexually dimorphic for reasons not yet known.